Field of the invention
The present invention relates to a register for indirect heat exchange between a utility fluid, in particular a flue gas, containing an interfering component, and a heat transfer fluid in a heat exchanger, with a plurality of tubes for the passage of the heat transfer fluid, wherein the tubes are arranged in a plurality of tube layers as well as a plurality of tube rows, wherein the tube layers and the tube rows run transverse to one another and wherein the tube layers define a plurality of flow channels for the flow through of the utility fluid. In addition the invention relates to a heat exchanger with at least one register, and also a use of the register.
Description of Related Art
Registers of a heat exchanger comprise a plurality of tubes and are also termed tube bundles. The tubes form tube layers arranged parallel to one another. In this way flow channels for the flow through of the utility fluid are formed between the tube layers. Transverse to the tube layers the tubes form so-called tube rows, which are likewise arranged parallel to one another. In a register of a heat exchanger the distances between the tube rows are constant just like the distances between the tube layers. A register is therefore constructed symmetrically. The structure of a register, i.e. the exact arrangement of the tubes with respect to one another, is described by the so-called pitch.
If the tube rows and the tube layers are aligned perpendicular to one another, this is then described as a square pitch if the tube rows and the tube layers are spaced equally far from one another. If this is not the case, then it is described as a rectangular pitch. For an accurate definition of the arrangement of the tubes in addition to the nature of the pitch the distance of the tube mid-points between two tube rows and two tube layers is also specified. With a square pitch it is therefore sufficient to specify one distance.
If the tube rows and the tube layers are not aligned perpendicular to one another, then this is described as a triangular pitch. The tube mid-points of three adjacent tubes then lie at the corners of a triangle, which may be, but does not have to be, an equilateral triangle. If the lengths of the sides of such a triangle are known, then the arrangement of the tubes in the register is just as uniquely fixed as when in the case of square or rectangular pitches the lengths of the sides of a square or rectangle formed by the tube mid-points of adjacent tubes are specified. Within a register the distances relating to the respective pitch do not alter. Registers with a square pitch and a triangular pitch are diagrammatically illustrated in FIGS. 1a and 1b for the sake of clarity.
Heat exchangers comprising such registers are known in various embodiments from practice and are referred to in particular as tube bundle heat exchangers. A heat exchanger can in this case comprise one or more registers. The heat exchangers are used for heat exchange between different fluids, which may be liquid or also gaseous. The fluid flowing through the register is hereinafter referred to as utility fluid, and the fluid flowing through the tubes of the register is referred to as heat transfer fluid.
If several heat exchangers are used in a process, then the utility fluid of a heat exchanger can if necessary be used as heat transfer fluid of another heat exchanger. In this case the utility fluid after leaving the one heat exchanger and before entering the other heat exchanger as heat transfer fluid is normally treated in a further process stage, such as a condensation or a separation of interfering components.
Heat exchangers are also known that operate in so-called cross-current. In this case the heat exchanger or at least a register is subdivided into two regions separated from one another, so that in the two regions different utility fluids flow around the tubes of the register. The flow directions of the utility fluids can in this case be opposite. The heat transfer fluid within the tubes of the register then in this case transports heat from one region of the register to the other region of the register, so that one utility fluid transfers heat to the other utility fluid. The utility fluids may be one and the same fluid stream at two different points in time during a technical process, for example for the processing, conditioning and/or cleaning of the fluid stream.
The heat exchangers and registers are used for example to cool or heat up a utility fluid in the form of a flue gas that is produced during combustion of a fuel. For this purpose the heat exchangers are for example integrated in a waste-gas purification plant. Heat exchangers designed to cool flue gases are for example connected in the form of a gas cooler upstream of a flue gas scrubber, whereas heat exchangers provided to heat flue gases can be connected downstream of a flue gas scrubber, in order to dry the flue gas. In this connection the temperature of the flue gas is raised to a higher level in order to prevent individual components condensing out in plant units connected downstream. Gas coolers as well as gas dryers can be provided in waste-gas purification plants.
Flue gases can, also like other media, contain a not inconsiderable amount of interfering components. These interfering components are predominantly particles, for example in the form of dusts. Interfering components may however also be liquids, such as for example condensate or wash liquid entrained on discharge from an upstream washer. The liquid is in this connection divided into a plurality of individual droplets. The condensate, especially in the treatment of flue gases, may be an acid or aqueous acidic solution. In addition the condensate can be introduced like other liquids and/or solids into the heat exchanger. The condensate can however also be formed first in the heat exchanger or in at least one register of the heat exchanger by a lowering of the temperature. In general a distinction is made in this case between the aggregate state of the interfering component and that of the utility fluid.
The interfering components in a utility fluid, such as for example a flue gas, may be homogeneous, for example of the same substance, or heterogeneous, composed of different substances.
The interfering components can coalesce in the heat exchanger, in particular in at least one of the registers of the heat exchanger, and collect there. Registers that are operated with utility fluids containing a relatively large concentration of interfering components should therefore be cleaned at regular intervals so that no blocking of the register occurs between individual tubes. Furthermore it can however also be undesirable if the interfering components are simply extracted with the utility fluid.
For the cleaning, a relatively large amount of rinse medium is often added to the utility fluid before entry to the register during operation, the rinse medium then being entrained by the flow of the utility fluid and carried through the register. This generally occurs at more or less regular, predetermined time intervals. The rinse medium can if necessary also be introduced uniformly distributed within the tube bundle of the heat exchanger. The rinse medium, which is generally water, should however in any case come into contact with the interfering components collecting in the register and remove these together with the rinse medium, in particular in the flow direction of the utility fluid, from the register.
So that the register has as small a tendency as possible for interfering components to collect and can at the same time be thoroughly cleaned, the register is constructed so that the utility fluid has a high flow velocity between the tube layers, which are aligned in a regular manner parallel to the outflow direction of the utility fluid. This is achieved in particular if the registers are constructed of tubes with relatively large diameters, which for this purpose are arranged at large distances from one another. In the end broad flow channels are thereby formed between the tube layers, which offer a low flow resistance to the utility fluid and through which utility fluid can thus rapidly flow.
Nevertheless it has been found in practice that the interfering components can collect to a large extent in the register, which can lead to the partial blockage or clogging of the register, for example in flow shadows between the tubes of a tube layer. This then means for example that continuously operating plants have to be shut down prematurely in order to service the register or clean it manually. This often leads in the case of hardening interfering components to damage to the tubes and/or to their corrosion protection due to the difficult and in some cases mechanical cleaning. This in the end leads to undesirable tube failures.